Thermoplastic polyamides, such as nylon 6,6, are a class of materials which possess a good balance of properties comprising strength and stiffness which make them useful as structural materials. However, for a particular application, a thermoplastic polyamide may not offer the combination of properties desired, and therefore, means to correct this deficiency are of interest.
One major deficiency of thermoplastic polyamides is their poor resistance to impact, especially when dry. A particularly appealing route to achieving improved impact resistance in a thermoplastic is by blending it with another polymer. It is well known that stiff plastics can often be impact modified by addition of an immiscible low modulus elastomer. However, in general, physical blending of polymers has not been a successful route to toughen thermoplastic polyamides. This is due to the poor adhesion immiscible polymers typically exhibit with each other. As a result, interfaces between blend component domains represent areas of severe weaknesses, providing natural flows which result in facile mechanical failure.
A route to achieve interfacial adhesion between dissimilar materials is by chemically attaching to one or more of the materials functional moieties which enhance their interaction. Such interactions include chemical reaction, hydrogen bonding, and dipole-dipole interactions.
It has been previously proposed to increase the impact strength of polyamides by addition of a modified block copolymer. Hergenrother et al in U.S. Pat. No. 4,427,828 and Shiraki et al in International Kokai Application No. WO83/00492 disclose blends of thermoplastic polyamide with a modified block copolymer. These blends are deficient, however, because the blended components, especially the block copolymer, are relatively expensive. Also, polyamides have a tendency to absorb water and consequently properties are degraded. Blending polyolefins with polyamides would decrease the water absorption for the blend since a portion of the polyamide which absorbs water would be replaced by polyolefin which absorbs relatively little water. In the past attempts to extend impact modified polyamides with polyolefins have been unsuccessful because the polyamides were incompatible with the polyolefins.
It has been discovered that by functionalizing various components in a polyamide-polyolefin-elastomer blend a desirable combination of properties and cost can be obtained.